Parking brake of a drum brake

ABSTRACT

A parking brake ( 10 ) having a drum containing first and second brake shoe portions ( 11, 12 ), a handbrake lever ( 18 ) pivoted ( 19 ) adjacent one end on one ( 11 ) of the brake shoe portions and a strut ( 20 ) extending between a first abutment on the handbrake lever and a second abutment ( 21 ) on the other ( 12 ) of the brake shoe portions. Pivoting of the handbrake lever relative to said one brake shoe portion ( 11 ) moves the strut ( 20 ) which in turn moves the other brake shoe portion ( 12 ) away from said one brake shoe portion to bring the shoe portions into contact with the drum thus applying the parking brake. One of the abutments is in the form of a biased wedging means ( 21 ) which acts on the strut ( 20 ) to take up all play in the thrust path between the handbrake lever ( 18 ) and the other brake shoe portion ( 12 ) via the strut. A clamping member ( 27 ) is provided for disabling the wedging means ( 21 ) from operating except when initial manufacturing or assembly clearances are being taken up in the strut or when a subsequent manual adjustment of shoe clearance is being made. Alternative snail-cam type wedging means ( 21 ) are also disclosed as in an electrically actuated parking brake system with an automatic clearance adjustment device.

This invention relates to parking brakes and in particular to parkingbrakes hereinafter referred to as of the type described which comprise adrum containing first and second brake shoe portions, a handbrake leverpivoted adjacent one end on one of the brake shoe portions, and a strutextending between a first abutment on the handbrake lever and a secondabutment on the other of the brake shoe portions so that pivoting of thehandbrake lever relative to said one brake shoe portion moves the strutwhich in turn moves the other brake shoe portion away from said onebrake shoe portion to bring the shoe portions into contact with the drumand thus apply the parking brake. The brake shoe portions may beprovided by separate brake shoes as in a normal twin shoe brake or byopposite end portions of a single shoe brake of the form disclosed in,for example, EP392829 or W099/53212.

Parking brakes of the type described are well known and work efficientlyparticularly when they are actuated manually by a conventional driveroperated lever. There is, however, an increasing requirement to provideparking brakes which are capable of electric motor application in orderto dispense with the conventional manually operated lever.

One problem associated with electric motor actuated parking brakes isthat the actuation system often has a relatively limited movementcapability and this can therefore provide difficulties in ensuringefficient and sufficiently long lived actuation of the parking brakefunction when teamed with a parking brake of the type described whichincludes significant inherent lost motion in its actuation linkage.

It is an object of the present invention to provide a parking brake ofthe type described which is suitable for electrical actuation.

Thus according to the present invention there is provided a parkingbrake of the type described in which one of the abutments comprises abiased wedging means which acts on the strut to take up all play in thethrust path between the handbrake lever and the other brake shoe portionvia the strut, means being provided for disabling the wedging means fromoperating except when initial manufacturing or assembly clearance arebeing taken up in the strut or when a subsequent manual adjustment ofshoe clearances is being made.

Such an arrangement with its biased wedging means can significantlyreduce the lost motion in the parking brake actuating linkage due tomanufacturing, assembly and adjustment clearances between the strut andthe first and second abutments and can also compensate for wear (due,for example, to Brinelling) of these components resulting from the highloads imposed on these components. Also the provision of the disablingmeans overcomes problems which can arise with such parking brakes if,when the parking brake is released, the brake shoes remain stuck to thedrum due to stiction since the wedging means will operate thus adjustingthe effective length of the strut into too long a condition andpreventing subsequent full release of the shoe portions from the drumeven if the stiction effect is overcome.

The means for disabling the wedging means may comprise, for example, areleasable clamping means which prevents movement of the biased wedgemeans relative to the co-operating abutment.

Typically the second abutment comprises a biased sliding wedge. One edgeof such a wedge may slide along a plate secured to the web of the otherbraking shoe portion, a further edge of the wedge sliding along afurther abutment surface on the strut. Preferably the further abutmentsurface on the strut comprises the root of a forked end portion of thestrut, the forked end having two prongs which extend on opposite sidesof a web of the other brake shoe portion.

Alternatively, the wedge means may comprise a cam rotationally biasedagainst one end of the strut by spring means.

In such arrangements the clamping means may comprise a clamping platewhich is drawn down onto the biased wedge or cam by a screw or bolt toclamp the wedge or cam to the web of the other brake shoe portion toprevent adjustment of the clearances.

Where the invention is applied to a twin shoe brake, the ends of thebrake shoes remote from the strut may pivot on a fixed reaction abutmentor on a manual or automatic wear adjustment device positioned betweenthe ends of the shoes. For example, where an automatic wear adjustmentdevice is used, the position of the shoes may be adjusted automaticallyto compensate for wear when a given amount of movement of the hand brakelever occurs before the brake is applied.

The invention also provides a parking brake system comprising anelectrical actuator, a parking brake of the form described above, andlinkage means connecting the actuator to the parking brake.

The invention further provides a parking brake system comprising adrum-type parking brake, an electrical parking brake actuator forapplying the parking brake, an actuating mechanism connecting theactuator to the parking brake, and an automatic parking brake clearanceadjustment device actuated when the movement of the actuating mechanismrequired to apply the parking brake exceeds a predetermined distance.

In such a system the parking brake may have first and second brake shoeportions and in which the actuating mechanism comprises a handbrakelever pivoted adjacent one end of the shoe portions, and a strutextending between a first abutment on the handbrake lever and a secondabutment on the other brake shoe portion so that pivoting of thehandbrake lever relative to said one brake shoe portion moves the strutwhich in turn moves the other brake shoe portion away from said onebrake shoe portion to bring the shoe portions into contact with a brakedrum and thus apply the parking brake, the automatic adjustment devicebeing provided between the ends of the shoes remote from the strut, andthe adjustment device being actuated by pivoting movement of thehandbrake lever relative to said one shoe portion beyond a predetermineddistance to increase the effective length of the adjustment device thusmoving the ends of the shoe portions apart to compensate for wear of theshoe portions.

In an alternative arrangement the parking brake may have first andsecond brake shoe portions and in which the actuating mechanismcomprises a first lever having a first contact zone adapted to engage aportion of the first brake shoe portion, said first lever beingpivotally connected with a second lever, the second lever having asecond contact zone adapted to engage a portion of the second brake shoeportion, pivoting of the first lever relative to the second lever beingarranged to increase the effective length of the mechanism between thecontact zones thus moving the associated brake shoe portions apart toengage the parking brake, the automatic adjustment device being actuatedby movement of one of the levers beyond a predetermined distance toincrease the effective length of the adjustment device thus compensatingfor wear of the shoe portions

In an alternative arrangement the parking brake may have a pair of shoesand the actuating mechanism may comprise a first lever having a firstcontact zone adapted to engage a portion of a first brake shoe, saidfirst lever being pivotally connected with a second lever, the secondlever having a second contact zone adapted to engage a portion of asecond brake shoe, pivoting of the first lever relative to the secondlever being arranged to increase the effective length of the mechanismbetween the contact zones thus moving the associated brake shoe portionsapart to engage the parking brake, the automatic adjustment device beingactuated by movement of one of the levers beyond a predetermineddistance to increase the effective length of the adjustment device thuscompensating for wear of the shoes.

The first and second brake shoe portions may be provided by separatebrake shoes or by appropriate end portions of a single generallyU-shaped brake shoe.

Several embodiments of the different aspects of the present inventionwill now be described, by way of example only, with reference to theaccompanying drawings in which:

FIG. 1 shows a perspective view of part of a twin shoe parking brake inaccordance with the present invention and;

FIGS. 2 and 3 show on a larger scale the clamped biased wedgingarrangement used in the parking brake of FIG. 1 in the initial brakeshoes unworn condition and in a subsequent brake shoes worn conditionrespectively;

FIG. 4 shows diagrammatically further details of the clamped biasedwedging arrangement of FIGS. 2 and 3;

FIG. 5 shows a perspective view of part of an alternative form ofparking brake in accordance with the present invention which uses acam-type adjuster;

FIGS. 6 and 7 show perspective views of two further forms of cam-typeadjusters;

FIG. 8 is a diagrammatic representation of an electrically actuatedparking brake system in accordance with the present invention;

FIGS. 9 to 12 show details of an automatic adjusting device for use aspart of a parking brake or parking brake system in accordance with thepresent invention;

FIG. 13 shows a view generally corresponding to FIG. 10 of a modifiedform of automatic adjustment device which includes a bi-metallic pawl;

FIGS. 14 and 15 show perspective and part sectional views respectivelyof an alternative form of automatic adjustment device;

FIGS. 16 to 20 show details of a further form of drum in disc typeparking brake in accordance with the invention which is also suitablefor use in the system of FIG. 8;

FIG. 21 shows diagrammatically the present invention applied to a singleshoe brake, and

FIG. 22 shows diagrammatically the parking brake actuating mechanism andautomatic adjustment device of the present invention located between thesame ends of a pair of brake shoes.

Referring to the drawings this shows part of a twin shoe parking brake10 for use in a so-called drum in disc brake in which a pair of shoes 11and 12 are mounted on a backplate 13. The upper ends of the shoes arepulled against a fixed backplate mounted abutment 14 (or against aseparate abutment on the adjacent vehicle suspension) by a return spring15 and the other ends of the shoes pivot on a wear adjustment deviceshown at 16 in FIG. 1. This wear adjustment device may be manuallyadjusted (as shown) or automatically adjusted, as will be describedbelow, in which the position of the shoes is adjusted automatically tocompensate for wear when a given amount of movement of the hand brakelever occurs before the brake is applied.

The shoes are contained within a drum (not shown) and the shoes arearranged to be brought into contact with the drum by an actuatingmechanism which comprises a handbrake lever 18 which is pivoted adjacentone end by pin 19 on brake shoe 11. A strut 20 which has forked ends 20a and 20 b acts between a first abutment 18 a on handbrake lever 18 anda second abutment associated with brake shoe 12 in the form of a plate22 which is riveted to the shoe 12 through rivets 24 and 25. A biasedwedge 21 acts between the root 20 c of forked end 20 b and plate 22. Areturn spring 29 acts between the lower ends 11 c and 12 c of shoes 11and 12.

The biased wedge 21 has one edge 21 a which slides down an edge 22 a ofplate 22 and a further edge 21 b which contacts the root 20 c of forkedend 20 b of strut 20. The wedge 21 is biased between the surface 22 aand the root 20 c by a wire spring 23 which encircles rivet 24 and hasone end 23 a engaging the wedge 21 and the other end 23 b engaging ahole 26 in plate 22 or reacting against plate 22.

In accordance with the invention a means for disabling the operation ofwedge 21 is provided in the form of a clamping plate 27 (which may beslightly arched as shown in FIG. 4) and which bears on wedge 21 and ispulled down onto wedge 21 by a nut or screw 28 having a head 28 alocated on the other side of brake shoe 12 as viewed in FIGS. 1 to 3.This head has a screw driver or other turning formation therein which isaccessible through a hole in the brake drum (not shown) so that thescrew can be slackened sufficiently to allow the wedge 21 to sliderelative to strut 20 and plate 22 when it is desired for any clearancebetween the handbrake lever 18, strut 20 and plate 22 to be taken up andwhich can be tightened to prevent sliding of the wedge 21 when it isdesired to prevent take-up of these clearances. The hole provided in thebrake drum to give access to the head 28 a of clamping screw 28 can alsobe positioned to give access to wear adjuster nut device 16 by rotatingthe drum appropriately.

Thus, if when the brake is initially assembled, the screw 28 is slack toallow the wedge 21 to slide relative to plate 22 any manufacturing orassembling clearances which may be present between the abutment surface18 a on handbrake lever 18 and the co-operating root 20 d of forked end20 a of strut 20 and between the root 20 c and the biased wedge 21 areautomatically taken up due to the biasing effect of the wire spring 23so that there I no lost motion in the parking brake actuating mechanism.Thus all pivoting of the handbrake lever 18 relative to the brake shoe11 by, for example, a cable 103, 104 which is attached to the lower end18 c of handbrake lever results in immediate movement of the strut 20and the other brake shoe 12. As explained above this is particularlyadvantageous if the brake is electrically actuated. FIG. 2 shows theposition of the wedge 21 after this initial take-up of clearances hasoccurred.

After this initial taking up of the clearances by the biased wedge 21the screw is tightened to clamp wedge 21 against shoe 12 and preventfurther adjustment of clearances by wedge 21. This, as explained above,avoids problems of over adjustment which would otherwise occur shouldthe shoes become stuck to the drum due to stiction.

If it is desired to manually adjust the shoe clearance due to wearduring servicing of the vehicle etc. using adjuster 16, for example, thewedge 21 can be reactivated during the adjustment by slackening screw 28to allow wedge 21 to slide under the action of spring 23.

It will be apparent that when adjuster 16 is operated to move the lowerends of brake shoes 11 and 12 apart to reduce the clearance of the shoesfrom the associated drum this will also result in the shoes movingslightly away from the ends 20 a and 20 b of the strut since the shoeseffectively pivot on the abutment between the upper ends of the shoes.This therefore tends to increase the clearances associated with strut 20and thus reactivation of wedge 21 helps to restore the overallefficiency of the actuating mechanism.

FIG. 3 shows the wedge 21 in a lower position relative to plate 22 aftera subsequent adjustment in the clearances associated with strut 20 hastaken place.

An alternative form of wedging means is shown in FIG. 5 in which asnail-type rotary cam 21 is pivoted on shoe 12 at 24 and has an edge 21a which is rotationally biased into contact with the root 20 c of theforked end 20 b of strut 20 by a wire torsion spring 23.

The cam 21 is disabled by a clamping member 27 which bears on the cam 21at 27 a and 27 b and is pulled down onto the cam 21 by a screw 28 havinga head 28 a on the other side of brake shoe 12 as viewed in FIG. 5. Theclamping member 27 is prevented from rotating relative to shoe 12 aboutscrew 28 by a pin 30 which engage a depression in the brake shoe 12.

Operation of snail cam 21 is similar to the sliding wedge 21 with thecam being released for operation by slackening screw 28 during theinitial taking up of clearances between the cam 21 and strut 20 and thenlocked during subsequent operation of the brake to prevent undesiredadjustment. Also the screw 28 can again be slackened during servicing ofthe vehicle etc when manual adjustment of the shoe clearance due to wearis being undertaken to again eliminate any clearances associated withstrut 20 which may have re-appeared.

FIGS. 6 and 7 show two further variations of the form of the clampingmember 27 used to disable the snail-type cam 21. In FIG. 6 the clampingmember 27 is prevented from pivoting about clamping screw 28 relative toshoe 12 by a projection 27 c which contacts the edged 12 e of shoe 12.In the FIG. 7 arrangement two projections 27 d and 27 e contact theinside 12 t of the table of the shoe 12 thus preventing rotation aboutclamping screw 28.

As indicated above the parking brake of the present invention isparticularly suited for use with electric actuators.

FIG. 8 shows a parking brake system in which two drum in disc typeparking brakes 10 of the form described above are operated by anelectrical actuator 100 under the control of a control system C.

The electrical actuator 100 may take any suitable form and, by way ofexample only, the actuator 100 illustrated diagrammatically in FIG. 8comprises a screw 101 connected with a brake operating linkage in theform of a cable 103 and a nut 102 connected with a second brakeoperating linkage in the form of a further cable 104.

The nut 102 can be rotated around the screw 101 by a motor 105 via agear system 106. Thus when the motor is rotated in one direction thescrew 101 is moved to the right as viewed in FIG. 8 and the nut 102 tothe left in FIG. 8 this draws the two cables 103 and 104 towards theelectrical actuator as indicated by arrows X in FIG. 8. Rotation ofmotor 105 in the opposite direction relaxes cables 103 and 104 torelease the brakes. Operation of motor 105 is under the control ofcontrol unit C which receives a variety of inputs including an inputfrom a driver operated button 107 positioned on the dashboard or at anyother convenient location of the vehicle and various other sensedparameters indicated generally at 108 which the control unit uses aspart of its control strategy for operating the motor 105. Since thedetails of the control strategy of control unit C and the constructionaldetails of the actuator 100 do not form part of the present invention nofurther details will be given.

Each drum in disc parking brake 10 may include an automatic wearadjustment means 16 between the lower ends of the shoes 11 and 12 aswill be described below.

The cables 103 and 104 can be attached to the lower ends 18 c ofhandbrake levers 18 by any suitable arrangement. For example thespring-loaded pivoting latch arrangement disclosed in the Applicant'sco-pending PCT application number WO 98/40640 may be employed in whichthe nipples 27 on cables 103 and 104 are fed into their latchedpositions shown in FIGS. 1 and 4 down the centre of a respective guidespring 18 e which also acts as a return spring for lever 18.

The wear adjustment means 16 comprises a variable length strut 30 (seeFIG. 9) in the form of a first strut member 31 having a diametrical slot31 a which receives the lower end 11 c of brake shoe 11 and which has ascrew threaded portion 31 b which is threadably received in a toothedratchet wheel 32. Screw threaded portion 31 b of strut member 31 isreceived with clearance in a bore 33 of a strut member 34 which also hasa diametrical slot 34 a which receives the lower end 12 c of shoe 12.Thus the strut members 31 and 34 are held against rotational movementrelative to the shoes 11 and 12 respectively and the effective totallength of the strut 30 can be varied by screwing the ratchet wheel 32along the screw threaded portion 31 b of strut member 31 since strutmember 34 reacts against the right hand side of ratchet wheel 32.

Thus in order to compensate for the wear of the linings 11 b and 12 b ofshoes 11 and 12 it is simply necessary to rotate the ratchet wheel 32 todisplace the lowers ends 11 c and 12 c of the shoes 11 and 12 away fromeach other to compensate for lining wear.

This adjustment of the effective length of the variable length strut 30is made automatically in response to the increasing movement ofhandbrake lever 18 relative to shoe 11 as the shoes wear. This increasedmovement is sensed by an adjusting lever 35 which is pivoted on shoe 11by rivet 36. Adjusting lever 35 includes a follower 37 which iscontacted by the lower edge 18 d of lever 18 when the handbrake isapplied by cable 103,104 and a pawl 38 which contacts the teeth ofratchet wheel 32. As will be appreciated, as the brake linings 11 b and12 b wear the movement of lever 18 necessary to apply the parking brakewill increase so that the lower edge 18 d of lever 18 will move furtherto the right as viewed in FIG. 9. This movement of the lower edge oflever 18 d causes follower 37 to pivot the adjusting lever 35 aboutrivet 36 in a clock-wise sense (see arrow P) as viewed in FIG. 9(counter clock-wise as viewed in FIGS. 10 and 11) to move the pawl 38 onlever 35 up and down the tooth 32 a which the pawl currently engages.Each time the handbrake lever is released and the lower edge 18 d movesback out of contact with follower 37 the adjusting lever 35 is pivotedback clockwise as viewed in FIGS. 10 about pivot 36 by a bias spring 39until a stop surface 35 a contacts the table 11 a of shoe 11.

Eventually the movement the follower 37 by the lower edge 18 d of lever18 results in sufficient movement of the pawl 38 up the contactingratchet wheel tooth 32 a to cause the pawl to slide over the top oftooth 32 a to engage the next tooth 32 b of the ratchet wheel. FIG. 12shows the pawl 38 about to pass over the top of tooth 32 a to engagetooth 32 b. On the next retraction of the lever 18 following theengagement of the new tooth 32 b the bias spring 39 rotates the ratchetwheel 32 anticlockwise (as viewed in FIG. 11 or 12) thus increasing theeffective length of strut 30 to adjust for the wear of the shoe linings11 b and 12 b which has occurred.

As will be appreciated the above parking brake system includes a simplebut effective means of continually adjusting for the wear of the linings11 b and 12 b of the brake shoes. This ensures that the free travelbefore the brake shoes contact the associated drum 17 is kept to aminimum which is of particular advantage when the parking brake isactuated electrically, as discussed earlier, since such electricallyactuation systems tend to have relatively limited travel. The wedge orcam 21 is disabled during normal operation of the parking brake functionbeing only operative during initial taking up of clearances associatedwith strut 20 and during manual adjustment of clearances duringservicing etc.

The parking brake 10 with its automatic wear adjuster 16 is alsosuitable for manual operation via, for example, a cable operated by aconventional driver operated lever and can also be used without thewedge or cam 21 when the elimination of clearances in the strut 20 isless essential.

Such an arrangement is a considerable improvement on current parkingbrake arrangements which require manual adjustment of the parking brakefunction which inevitably leads to the parking brake becoming lesseffective than desirable between the normal service intervals of thevehicle.

FIG. 13 shows a modification of the arrangement shown in FIGS. 9 to 12in which the pawl 38 formed integrally with adjusting lever 35 isreplaced by a bi-metal pawl 40 arranged so that should the generaltemperature of the parking brake become excessively high (which mightlead to over adjustment of the clearances etc.) the bi-metal pawl willtend to bend away from the ratchet wheel teeth thus disengaging theteeth and preventing any adjustment of the effective length of strut 30until the temperature of the brake has fallen to a level at which thebi-metal element once again engages the ratchet wheel teeth.

FIGS. 14 and 15 show an alternative arrangement in which instead ofusing the bias spring 39 to provide the motive force for rotating theratchet wheel 32 the teeth on ratchet wheel 32 are reversed so that themovement of the handbrake lever 18 and its co-operation with thefollower 37 is arranged to pivot the adjusting lever 35 anti-clockwiseabout the rivet 36 when viewed in FIG. 14 thus causing the end of pawl38 to contact the root portion 32 c of tooth 32 a and thus rotate theratchet wheel 32 slightly in a clockwise sense as viewed in FIGS. 14 and15. Thus each time the lower edge 18 d of handbrake lever 18 moves upfollower 37 there is a tendency for the ratchet wheel 32 to be rotatedslightly in a clockwise sense if any wear of the associated brake shoeshas taken place. On each retraction of the handbrake lever 18 the spring39 draws the end of pawl 38 up the ramp 32 d of the next tooth 32 b asthe adjusting lever 35 is moved back so that its stop surface 35 acontacts the table 11 a of shoe 11. Eventually the clockwise rotation ofthe ratchet wheel resulting from and the coaction of the lower edge 18 dof lever 18 and follower 37 will have rotated the ratchet wheel 32sufficiently clockwise as viewed in FIGS. 14 and 15 so that, onretraction of the adjusting lever 35 by spring 39, the end of pawl 38rides over the tip 32 e of tooth 32 b and engages the root 32 f of thenext tooth 32 b. Thus there is a continuous small rotation of ratchetwheel 32 as the associated brake shoes 11 and 12 wear.

In the arrangement shown in FIGS. 14 and 15 the pawl 38 is of abi-metallic construction, similar to that shown in FIG. 13, which isriveted to the adjusting lever 35 and which will disengage the teeth ofratchet wheel 32 if the temperature of the parking brake becomesexcessive in order to prevent over adjustment of the effective length ofstrut 30.

As will be appreciated, the inclination of the lower edge 18 d of lever18 which is contacted by follower 37 may be varied to adjust the amountof pivoting of adjusting lever 35 corresponding to a given amount ofmovement of lever 18. Also, the follower 37 could be replaced by a camformation on plate 35 for co-operation with lever 18 to again produce aparticular relationship between the pivoting of adjusting lever 35 andhandbrake lever 18.

FIGS. 16 to 20 show an alternative form of automatically adjustingparking brake in accordance with the present invention which uses anexpanding lever actuating mechanism 200 similar to that described in theApplicant's co-pending published PCT patent application No. WO01/21976A1 and the Applicant's earlier UK patent application No. 0203894.1.

This expander mechanism 200 is positioned between the upper ends ofbrake shoes 11 and 12 and comprises a first lever 211 having a firstcontact zone 212 for engagement with a web of an associated brake shoe11 and a second lever 215 having a second contact zone 216 forengagement with the web of a second brake shoe 12. The two levers 211and 215 are pivotally interconnected at 219 so that, in conventionalmanner, pivoting of first lever in direction P1 results in an increasein the distance between the first and second contact zones 212 and 216to force the brake shoe 11 and 12 apart causing them to engage with anassociated drum in disc 10 a. As is conventional, the brake includesreturn springs 220 and 29 which act between the shoes and an automaticadjustment device 16 generally of the form described above in relationto FIGS. 9 to 12, or 13, or 14 and 15 is located between the lower ends11 c and 12 c of the brake shoes.

The shoes 11 and 12 are mounted on a back plate 213 which includes anaperture 224 through which a parking brake actuating cable 225 extends.The cable has an outer sheath 226 which is gripped in aperture 224 andan inner member 227 whose free end terminates in a nipple 228. As can beseen from FIGS. 18 to 20, first lever 211 is of hollow pressed metalform and includes a longitudinally extending passage 229 whose crosssection includes a wider portion 230 (see FIG. 20) through which thenipple 228 can pass and a narrower portion 231 through which the nipplecannot pass. As shown in FIG. 19, the inner 227 of the cable can bethreaded through the wider portion 230 of passage 229.

A leaf spring 240 is mounted on lever 211 in a notch 241 by clip portion242 and tabs 243. Spring 240 includes a cam portion 244 which iscontacted by the nipple 228 as the nipple emerges from the passage 229and which tends to deflect the nipple 228 towards a fully installedposition shown in FIG. 19 in which a shoulder 233 of nipple 228 contactsan end 231 a of the narrow portion 231 of passage 229 when the cableinner 227 is drawn in direction Z of FIG. 20 so that the first lever 211is pivoted in direction P1 and hence the actuating mechanism isoperated. End 231 a of narrow passage portion 231 forms the abutmentformation of lever 211.

The expander mechanism 200 is connected with the automatic adjustmentdevice 16 by a link and bell crank arrangement shown in FIGS. 16 and 17.This link and bell crank arrangement which comprises link 250 directlyconnected with lever 211, bell crank 251 pivoted on the brake backplateabout an axis 252, further links 253 and 254 and an intermediateconnecting bell crank 255 which is again pivoted on a brake backplateabout an axis 256. The final link 254 is connected with adjusting lever35 so that pivoting of lever 211 in direction P1 is translated intodownward movement of adjusting lever 35 as indicated by arrow S in FIG.17.

Thus when the pivotal movement P1 of lever 211 exceeds a pre-determinedamount there is sufficient vertical movement S of adjusting lever 35 toride over onto the next tooth 32 b on ratchet wheel 32. Thus again thewear of linings 11 b and 12 b of shoes 11 and 12 is automaticallyadjusted when the movement of the handbrake actuating mechanismnecessary to apply the handbrake exceeds a pre-determined distance.

The automatically adjusting parking brake described in FIGS. 16 to 20may be manually actuated by cable 225 or this cable may be electricallyoperated when the parking brake described in FIGS. 16 to 20 is used aspart of a parking brake system as shown in FIG. 8.

The automatically adjusting parking brake concept of the presentinvention in which movement of the parking brake actuating mechanismbeyond a pre-determined distance is used to effect adjustment of thebrake shoe clearance may be implemented by locating both the handbrakeactuating mechanism and the automatic wear adjuster at the same end ofthe brake shoe of shoes.

Thus, for example, as shown diagrammatically in FIG. 21 in a single shoedrum brake of the type, for example, disclosed in EP 392829A1 andWO99/53212 both the parking brake actuating mechanism 300 and theautomatic wear adjuster 316 may be located between the free ends 311 aof a single curved generally U-shaped brake shoe 311.

Similarly, as shown diagrammatically in FIG. 22, in a two shoe brakewith a fixed or floating abutment 414 located between the lower ends ofbrakes shoes 411 and 412 the parking brake actuating mechanism 400 andautomatic wear adjuster 416 may be located between the upper ends 411 aand 412 a of the shoes.

In both of the arrangements described above in relation to FIGS. 21 and22 movement, for example, of part of the parking brake actuatingmechanism in direction R could be used to pivot an adjuster leversimilar to adjuster lever 35 described above in relation to FIGS. 9 to12 to move a pawl similar to pawl 38 to rotate a ratchet wheel 332 or432 respectively.

Thus the present invention provides an electrically actuated drum typeparking brake in which operation of a parking brake actuating mechanismis used to automatically adjust the shoe clearance of the parking brakewhen a given amount of movement of the actuating mechanism occurs beforethe shoes are applied. The invention is particularly, although notexclusively, applicable to drum in disc parking brakes.

1. A parking brake comprising a drum containing first and second brakeshoe portions, a handbrake lever pivoted adjacent one end on one of thebrake shoe portions and a strut extending between a first abutment onthe handbrake lever and a second abutment on the other of the brake shoeportions so that pivoting of the handbrake lever relative to said onebrake shoe portion moves the strut which in turn moves the other brakeshoe portion away from said one brake shoe portion to bring the shoeportions into contact with the drum thus applying the parking brake, oneof the abutments comprising a biased wedging means which acts on thestrut to take up all play in the thrust path between the handbrake leverand the other brake shoe portion via the strut, means being provided fordisabling the wedging means from operating except when initialmanufacturing or assembly clearances are being taken up in the strut orwhen a subsequent manual adjustment of shoe clearance is being made,wherein the biased wedging means comprises a cam rotationally biasedagainst one end of the strut by a spring means.
 2. A brake according toclaim 1 in which the first and second brake shoe portions are providedby separate brake shoes.
 3. A brake according to claim 1 in which thefirst and second brake shoe portions are provided by opposite endportions of a single generally U-shaped brake shoe.
 4. A brake accordingto claim 2 in which the ends of the brake shoes remote from the strutpivot on a brake shoe clearance adjustment device are positioned betweenthe ends of the shoes and in which the biased wedging means is a slidingwedge.
 5. A brake according to claim 4 in which the adjustment deviceoperates automatically when a given amount of movement of the hand brakelever occurs before the brake is applied.
 6. A brake comprising a drumcontaining first and second brake shoe portions, a handbrake leverpivoted adjacent one end on one of the brake shoe portions and a strutextending between a first abutment on the handbrake lever and a secondabutment on the other of the brake shoe portions so that pivoting of thehandbrake lever relative to said one brake shoe portion moves the strutwhich in turn moves the other brake shoe portion away from said onebrake shoe portion to bring the shoe portions into contact with the drumthus applying the parking brake, one of the abutments comprising abiased wedging means which acts on the strut to take up all play in thethrust path between the handbrake lever and the other brake shoe portionvia the strut, means being provided for disabling the wedging means fromoperating except when initial manufacturing or assembly clearances arebeing taken up in the strut or when a subsequent manual adjustment ofshoe clearance is being made, wherein the means for disabling thewedging means comprises a releasable clamping means which preventsmovement of the biased wedging means relative to the co-operatingabutment, and wherein the clamping means comprises a clamping memberwhich is drawn down onto the biased wedging means or a cam by a screw orbolt to clamp the wedging means or the cam to the web of the other brakeshoe portion to prevent adjustment of the clearances.
 7. A brakecomprising a drum containing first and second brake shoe portions, ahandbrake lever pivoted adjacent one end on one of the brake shoeportions and a strut extending between a first abutment on the handbrakelever and a second abutment on the other of the brake shoe portions sothat pivoting of the handbrake lever relative to said one brake shoeportion moves the strut which in turn moves the other brake shoe portionaway from said one brake shoe portion to bring the shoe portions intocontact with the drum thus applying the parking brake, one of theabutments comprising a biased wedging means which acts on the strut totake up all play in the thrust path between the handbrake lever and theother brake shoe portion via the strut, means being provided fordisabling the wedging means from operating except when initialmanufacturing or assembly clearances are being taken up in the strut orwhen a subsequent manual adjustment of shoe clearance is being made,wherein the brake is of the drum in disc type.
 8. A brake according toclaim 7 in which the biased wedging means is a sliding wedge.
 9. A brakeaccording to claim 8 in which the wedge slides along a plate secured toa web of the other brake shoe portion, a further edge of the wedgesliding along a further abutment surface on the strut.
 10. A brakeaccording to claim 9 in which the further abutment surface on the strutcomprises the root of a forked end portion of the strut, the forked endhaving two prongs which extend on opposite sides of the web of the otherbrake shoe portion.